Direct reduction of iron-oxide ore in fine, lump, and pellet form is well known in metallurgical literature and patents for processes involving rotary kilns, shaft furnaces, fluidized beds, and retorts of various sizes and shapes. In general, such processes have evolved for the purpose of directly reducing ironoxide ore in solid-state form to metallized iron, commonly known as directly reduced iron, or "DRI", which can be easily melted in an electric arc furnace to produce high quality steel, having a low percentage of residual elements, or gangue.
"Metallized", as used throughout this specification does not mean coated with metal, but means nearly completely reduced to the metallic state, i.e., always in excess of 60% metal, and usually in excess of 90% metal in the material. Such metallized iron in many forms, including pellets, is well suited as feed material to steelmaking furnaces such as an electric arc furnace.
Existing direct reduction processes are generally intended for high tonnage production rates on a continuous basis, with the end product being high grade DRI with metallization levels about 92 to 94 percent, and having a maximum residual gangue content of less than eight percent. While rotary kilns, in general, utilize solid forms of carbon such as lignite, coal, or coke to provide the reductant source, shafts furnaces, retorts, and fluidized bed furnaces normally utilize natural gas or oil to provide the reductant source.
Recent advancements in plasma melting technologies have resulted in the development of several new smelting processes capable of directly reducing and melting iron-oxide ore to produce pig iron or steel. These new processes for the most part are still in the experimental stage of development, and are dependent on low power costs to be economical. Plasma processes in the field of electric arc furnace flue dust reprocessing are primarily designed to recover only zinc and lead in crude metallic form while the iron contained in the material is melted in oxide form and becomes inseparable from the slag which must then be disposed of as solid waste.
Existing direct reduction processes designed to produce large annual tonnages of DRI for use as a remelt stock in electric arc furnaces steelmills, in general, cannot be economically downsized to meet the needs for "on-site" reprocessing of small tonnages of flue dust material. Recent development of direct reduction and direct smelting processes such as rotary kiln, rotary hearth, retort, and plasma furnaces each have possible on-site application where the economy-of sale is favorable. An apparatus and process which provides distillation and recovery of the heavy metal oxides contained in electric arc furnace flue dust as well as recovering metallic iron in the form of either DRI, or pig iron from the resulting slag on a small scale and at a low capital and operating cost would be beneficial. The majority of mini-steelmills, both in the United States and in the rest of the world, produce less than 10,000 tons per year of flue dust each.
The Resource Conservation and Recovery Act of 1976 ("RCRA"), and the NEW RCRA Hazardous and Solid Waste Amendments of 1984 for handling and disposing of waste materials listed by the U.S. Environmental Protection Agency as hazardous, establishes certain guidelines and deadlines with which producers of hazardous waste materials must be prepared to comply by Oct. 8, 1988. The Comprehensive Environmental Response, Compensation, and Liability Act ("CERCLA") establishes potential liabilities for clean-up of existing hazardous waste disposal sites and inorder to ensure compliance with these regulations as well as future regulations, and to avoid potential future liabilities, it is imperative that all producers of hazardous waste materials in "on-site" facilities in the future.
In view of existing technology available, and the economics of applying such technology, there remains the need for simple, low cost, safe, and effective processes for the treatment and conversion of waste materials classified as hazardous by the EPA into recycable or non-hazardous disposable materials.